U.N. Syria envoy Staffan de Mistura says if he can restart intra-Syrian talks in July, there still is a possibility of moving forward on a political transition by an August deadline.

“I’m still aiming, we are aiming within July, but not at any cost and not without some guarantees; and aiming at August as the period where we should be seeing something concrete, so that in September we take stock,” de Mistura told reporters after he briefed the U.N. Security Council in a closed session Wednesday.

He underscored that the next round of talks must be very well prepared because they likely will be the last before world leaders convene for their annual meetings in New York in mid-September.

De Mistura noted that the September General Assembly session will be the final one for outgoing U.N. Secretary-General Ban Ki-moon, as well as for U.S. President Barack Obama. The G20 summit also is planned for early September in China, and that could be the last time Obama and Russian President Vladimir Putin meet.

The United States and Russia co-chair the International Syria Support Group (ISSG), and each back major parties to the conflict. Moscow supports Syrian President Bashar al-Assad and Washington backs moderate opposition groups.

FILE - Girls walk near a Red Crescent aid convoy carrying urgent medical supplies in the rebel-held besieged town of Douma, near in Damascus, Syria, May 26, 2016.

Turning on the pressure

“Yes, I am putting pressure on all parties,” de Mistura told reporters. “I think that the main parties who can make this happen need to feel that they have an historic responsibility.”

An August 1 deadline is looming over the talks, imposed by a U.N. Security Council resolution and backed by the ISSG. The resolution sets August 1 as the target date for the parties to reach agreement on a framework for a genuine political transition, which would include a broad, inclusive, non-sectarian transitional governing body with full executive powers.

“What we need is that the stakeholders do come with a feeling of urgency and work on some ideas on how to bridge their differences between what everyone means by political transition,” de Mistura said.

On the humanitarian front, de Mistura welcomed the news that all 18 besieged areas of Syria have now been reached with aid.

The U.N. announced Wednesday that it had finally succeeded in reaching the remaining two besieged towns on a list of 18 locations in Syria. The towns of Arbin and Zamalka received their first aid deliveries since November 2012.

The U.N. and its partners have now been able to access all 18 besieged locations in Syria through cross-line operations and airdrops.